1. Technical Field
The present invention relates to a monolithic duplexer, and more particularly to a monolithic duplexer that includes transmitting/receiving part filters, each including a resonator and a trimming inductor formed on a substrate and a phase shifter, which is formed on a packaging substrate, for preventing signal interference between the transmitting/receiving part filters, and a fabricating method thereof.
2. Related Art
A duplexer is a related art element that compositely uses a filter, and serves to efficiently share an antenna by properly branching transmitted/received signals through the same antenna in an FDD (Frequency Division Duplex) type communication system.
The duplexer includes a transmitting-end filter and a receiving-end filter. The transmitting-end filter is a band pass filter that passes only a frequency subject to transmission, and the receiving-end filter is a band pass filter that passes only a frequency subject to reception. By passing specified frequency band signals through the respective filters, one antenna can efficiently be shared. This duplexer is used in various kinds of RF appliances that perform wireless communication.
Particularly, the related art mobile phone has been improved in function and size. More specifically, a subminiature, high-sensitivity and multifunction mobile phone has recently been developed. Consequently, it is also necessary to fabricate a small-sized, light-weight filter or duplexer that is used in the mobile phone. Accordingly, an FBAR (Film Bulk Acoustic Resonator) manufactured using an MEMS (Micro-Electro-Mechanical Systems) technology has recently been used for filter or duplex fabrication. The FBAR can be mass-produced with a minimal cost and size. Additionally, the FBAR has a high quality factor Q that is the main characteristic of the filter, and can be used in a micro-frequency band as well as in PCS (Personal Communication System) and DCS (Digital Cordless System) bands.
Meanwhile, since the frequencies of signals transmitted/received through the transmitting-end filter and the receiving-end filter are slightly different, they react sensitively to each other to cause signal interference between them. To solve this, the duplexer further includes a phase shifter for isolating the transmitting/receiving part filters from each other. The phase shifter is typically implemented by a combination of a capacitor and an inductor that generates a frequency phase difference between the transmitted signal and the received signal of 90 degrees to prevent the mutual influence exerted between them.
FIG. 1 is a vertical sectional view illustrating the structure of a duplexer fabricated according to a related art method. The related art duplexer includes a printed circuit board (PCB) 10, a phase shifter 20, a transmitting-end filter 30 and a receiving-end filter 40. In this case, the phase shifter 20, transmitting-end filter 30 and receiving-end filter 40 are formed as separate elements, and are bonded on the PCB 10. The connection among the transmitting/receiving part filters 30 and 40 and the phase shifter 20 is made by a wire bonding method. According to the duplexer fabricated by the method illustrated in FIG. 1, respective internal elements are separately formed, packaged and then combined into one. Accordingly, the whole fabricating process is complicated, and the size of the finally fabricated duplexer becomes larger. Additionally, since the respective elements are connected together by the wire bonding method, signal loss may occur due to parasitic components produced in the wire parts. Consequently, the duplexer illustrated in FIG. 1 has at least the drawback in that it is disadvantageous to use the duplexer in a small-sized, high-performance appliance such as a mobile phone.